The present invention relates, in one aspect, to a poly-hydroxynaphthalene compound which is of value as an epoxy resin curing agent or an epoxy resin precursor, and in another aspect, to a highly dependable epoxy resin composition for use as a semiconductor encapsulant.
To protect semiconductor elements against the external environment, it is common practice to encapsulate them with an epoxy resin composition. This composition generally comprises an epoxy resin, a curing agent, a curing accelerator or promoter, a filler and several additives. The epoxy resin is an epoxidized version of a novolac resin which is obtainable by reacting a phenolic compound with formaldehyde and is typically an epoxidized o-cresol novolac. As the curing agent, phenol-formaldehyde novolac resin is typically employed. Further, as highly efficient curing agents, novolac resin obtained by reacting .alpha.-naphthol with aldehyde compounds, and epoxy resin derived from said novolac resin are known. But they have rather high softening points and fusion viscosities to be subjected to further processes such as molding, hence have not been put to practical use. On the other hand, it is known that .beta.-naphthol which has poor reactivity to aldehyde compounds cannot be adopted.
The increasing density and size of semiconductor elements and the implementation of multi-pin flat packages in recent years are tending to reduce the amount of epoxy resin relative to the encapsulated semiconductor element. As a consequence, the semiconductor is more likely to be exposed to large stresses in the encapsulating operation. Moreover, as the surface-mounting method involves dipping of the encapsulated semiconductor in a molten solder bath, the semiconductor is not only subjected to intense thermal stresses but exposed to the adverse environment such that the water within the resin is rapidly vaporized to cause an expansion of resin volume.
When a large capacity semiconductor is encapsulated with the above epoxy resin, the problem of a cracked package may occur, causing deformation or corrosive breakage of the bonding wire and cracking of the passivation film of the element. Therefore, several high-performance epoxy resins have heretofore been proposed but none have overcome the problems.
It is an object of the present invention to provide a poly-hydroxynaphthalene compound which is of use as a curing agent for epoxy resin or an epoxy resin precursor and capable of providing a cured body which has a high glass transition temperature and improved heat and moisture resistance and is able to prevent cracking of a semiconductor package.
It is another object of the invention to provide a novel epoxy resin composition and an epoxy resin, which have a high glass transition temperature and improved heat and moisture resistance and are adapted to prevent cracking of a semiconductor package.
It is still another object of the invention to provide an epoxy resin composition and an epoxy resin, which are of use as a semiconductor encapsulant.